Synthesis of vitellogenin polypeptides and deposit of yolk proteins in Anolis pulchellus

Abstract

The recognition of liver and serum polypeptides in Anolis pulchellus by a polyclonal antibody against S1-lipovitellin confirmed their identity as vitellogenins (Vtg) and demonstrated their structural relationship to yolk lipoproteins. In vivo labeling demonstrated active synthesis of Vtg by vitellogenic females since intracellular incorporation of [ 3h]-leucine was detected at short periods of label in all five Anolis Vtg forms. Time course analysis of 3H-Vtg levels indicated a 1 hr lag phase between synthesis and secretion. On the other hand, 32P-Vtg appears to be rapidly secreted from the liver into the blood since label was detected simultaneously in both compartments. After 2 hr intracellular 32p-Vtg levels reached a plateau. Decreasing 32P-Vtg levels in the blood were observed several hours after injection. In growing oocytes 32P was detected in yolk phosphoproteins ranging from 37,000 to 75,000 in molecular weight. Based on these results together with previous published data we conclude that in tropical anole the yolk phosphoproteins appear to be derived from the larger highly phosphorylated Vtg forms according to the typical vertebrate Vtg precursor-product relationship. However, the main component of yolk lipovitellin is synthesized in the liver as an independent lipoprotein (Vtg-116) which is taken up by growing oocytes without major proteolytic modifications. This novel mode of lipovitellin biosynthesis and deposit in reptiles has not been reported previously.